Algorithms

 When using the flat terrain version of the model, a release is simulated as a series of puffs. There are three algorithms used for motion and dispersion of a release in the atmosphere. The model, using the currently calculated parameters of a release, internally decides on the use of an algorithm. The algorithms cover: the jet phase of the release (all densities), the gravitational spread when a denser-than-air cloud is on the ground, and all other cases (e.g. not denser-than-air on ground and aloft clouds).

 When using the complex terrain version of the model, the motion and dispersion of the release is determined through the use of fundamental equations of Navier-Stokes.

 The fire algorithms calculate the thermal radiation impact from BLEVEs, Jet Fires or Flares, and Pool Fires. For Jet and Pool Fires effects such as flame tilt are calculated.

 Two forms of explosion are allowed: Mechanical Failure and Vapor Cloud Explosions. A Mechanical Failure simulation assumes a pressurized containment vessel fails instantaneously, releasing a pressure wave. The Vapor Cloud Explosion algorithms can handle deflagration and detonation.

A complete description of the algorithms used in the flat terrain version of the software is available.

A complete description of the algorithms used in the complex terrain version of the software is available.

A schematic of the processes considered within a grid cell for the complex terrain version is shown below in Figure 1.

 Figure 1. Processes considered in the complex terrain version of CHARM..